Well, your pics just full on sold me on the carriage bolt idea. I checked at Home Depot today and couldnt find any chrome ones.

Side note: What size carriage bolts are those?

I got them at ace and I believe they are 5/16 X 1, also used the nyloc nut and three washers on each bolt because of the square on the back of the bolt....the washers need to go over it to make it sit tight against the bumper.

The 5/16 that I got had a square almost the same size as the bumper, without being too big